Pipe bursting is a well known process that brings enormous potential for the efficient and unobtrusive replacement of buried pipelines. Static bursting systems have been used for that purpose. Such systems pull or push a string of rods through the ground or existing pipeline. See for example Handford U.S. Pat. No. 5,205,671. Such systems generally provide a mechanism for both pulling/pushing the rod string and for adding and removing sections of rod to-the end of the string. Most commonly, the rod strings used by these machines are made from consecutive cylindrical steel rods that are threaded together end to end as the rod string advances through the ground. Spinner mechanisms used to thread and unthread rods are known in the art, such as shown in the Handford patent cited above.
More recently static bursting systems have been proposed that make use of rods with radial protrusions or upsets intended to be grasped by the pipe pushing-pulling mechanism. One such mechanism is described in commonly-assigned U.S. Ser. No. 10/916,117, filed Aug. 11, 2004, United States Patent Application 20060034666, Feb. 16, 2006, the entire contents of which are incorporated herein by reference. The described method relies on rods that have enlarged shoulders. Another system for pushing and pulling rods with annular flanges is described in Puttman U.S. Pat. No. 5,980,157.
A need has emerged for a simple and durable mechanism for pushing or pulling a string of rods as part of an earth boring or pipe bursting operation, especially rods with radial protrusions or upsets intended to be grasped by the pipe pushing-pulling mechanism in a manner that provides reduced wear and slippage. The present invention addresses this need.